Control circuits for cathode-ray tubes



Sept. 30, 1952 J. E. SHEPHERD ET AL 2,612,621

CONTROL cmcurrs FOR CATHODE-RAY TUBES Filed June 18, 1942 2 SHEETS SHEET 1 Earl.

INVENTORS, JAMES E. SHEPHERD, and CHARLES H GUILES;

TH EIR ATTORNEY- Sept. 30, 1952 J. E. SHEPHERD ET AL 2,612,621

CONTROL CIRCUITS FOR CATHODE-RAY TUBES Filed June 18, 1942 2 SHEETS-SHEET 2 108 Ill INVENTORS, JE:....3 JAMES E. SHEPHERD, and

CHARLES H GUJLES;

THEIR ATTORNEY Patented Sept. 30, 1952 CONTROL CIRCUITS FOR GATHODE-RAY TUBES James E. Shepherd, Hempstead, and Charles H. Guiles, East Hempstead, N. Y., assignors to The Sperry Corporation, a corporation of Delaware Application June 18, 1942, Serial No. 441,534

The present invention relates to the art includ ing cathode ray tube control circuits.

For producing bright indications on a cathode ray screen, high accelerating voltages are required, resulting in low deflection sensitivity. Under these conditions, large deflecting voltages are required to completely move the trace from one side of the cathode ray tube screen to the other. These voltages may be of the order of 700 volts. Systems are known in which a single amplifier provides this deflecting voltage.v However, a large voltage requirement of this sort generally exceeds the voltage rating of the power supply and of the tube itself for tubes ordinarily used in such devices. A further disadvantage of prior art devices resides in the fact that, with high accelerating voltages, serious de'-focusing of the spot trace may result unless the average voltage of each pair of deflecting plates .is kept approximately constant.

These disadvantages may-be overcome by the use of push-pull amplifiers for supplying the defleeting potentials, whereby the maximum voltage of each deflecting plate is reduced to substantially half that required from a single amplifier, permitting the use of commercially available tubes and power supplies, and whereby, further, the average potential of each pair of plates is kept substantially fixed.

Where it is desired to control a cathode ray tube by two distinct inputs to alternately produce corresponding traces on the screen of the cathode ray tube at a rate sufiiciently high to render these traces simultaneously visible, as in the presentinvention, further problems are encountered. In many prior systems, alternating current ampliflers for the input control voltages are used, upon whose output is superposed a uni-directional voltage for determining the average spot position. Where it is desired to superpose two ormore indications, such a system suffers the'disadvantage that the average or centralpositions of all the cathode ray patterns are controlled simultaneously and cannot be independently controlled.

In order to avoid this difliculty, the present invention uses a direct current amplifier for supplying the complete deflecting potentials required. This amplifier is of the push-pull type for the reasons discussed above and is controlled by an electronic switch having separate switching" tubes which alternately provide respective control voltages to be applied to the deflecting plates ofthe cathode ray tube by this amplifier. Separatelunidirectional pattern positioning voltages maybe 21 Claims. (01. 315-23) 2 V that the respective cathode ray patterns p oduced on the screen of the tube may be independently positioned by simplelow voltage positioning controls, without being afiected by the positioning control for any other pattern.

The present invention thus provides an efiicient and desirable device whereby two or more rapidly v r ng voltages, which, for example, may comprise a high frequency test voltage and a sweep voltage, or a test voltage and a timing wave, may be simultaneously viewed on a cathode ray screen, and each pattern may be positioned independently on the screen.

In addition, it may be desirable in some cases to change the position of any or all patterns at some slow rate. This may be easily accomplished by the system of the invention by superimposing a low frequency alternating voltage on the pattern-positioning voltages already fed through the switching tube. Such a system is inherently capable of extremely fast switching action, and renderslitself readily applicable to the simultaneous viewing of rapid recurrent transient phenomenon and other phenomena on the same screen without loss in brilliance of the transient pattern.

Thus, in previous slower acting systems, the transient pattern, for example, would be placed on the screen for half the total time and the other pattern for the remaining time. In the present system, however, the switching period may be made equal to the recurrence period of the transient henomenon and synchronized with it. Thereby the transient phenomenon pattern may be switched on at each occurrence thereof, and, if it persists for an interval less than half the switching period, will be projected completely on the screen during each of its occurrences,

without affecting the usefulness of the screen for showing the other phenomenon during the portions of the switching period when the transient phenomenon does not occur. In this manner, the brilliance of the transient pattern is the same as though the entire cathode ray tube were devoted solely to its presentation, as distinguished from prior systems in which the transient period :can be only a fraction as bright because of its appearance onthe screen for only a fractional time.

Accordingly, it is an object of the present invention to provide improved control circuits for cathode ray tubes.

It is another object of the present invention to provide improved control circuits for cathode ray tubes controlled by a plurality of input voltages.

It is a further object of the present invention to provide improved control circuits for the 'defleeting plates of the cathode ray tubes controlled by a plurality of input voltages and providing independently positlonable traces upon the screen of the cathode ray tube.

It is still another object of the present invention to provide improved control circuits for the deflecting plates of cathode ray tubes employi push-pull direct-coupled amplifiers.

It is a still further object of the present invention to provide improved control circuits for the deflecting plates of cathode ray tubes employing push-pull direct-coupled amplifiers v plural input voltages, wherein the average output potential of said commutating system for each of said input voltages may be independently adjusted.

It is yet another object of the present invention to provide an improved electronic switching circuit underthe control of a switching voltage, in which thejcircuit is rendered substantially independent of fluctuations inmagnitude of the switching voltage.

It is still a further object of the present invention to provide improved apparatus for rendering anelectronic discharge tube'alternately conductive and non-conductive while maintaining substantially constant the average output voltage thereof. v

It is still another object of the present invention to provide improved apparatus for rendering a pair of electron discharge tubes alternately and oppositely conductive and non-conductive while maintaining substantially constant the average output potential of eachof the tubes.

Other objects and advantages will become apparent from the specification, taken in connection with the accompanying drawings wherein the invention is embodied in concrete form.

In the drawings,

Fig. 1 shows a circuit diagram of one embodiment of the present invention. I

Fig. 2shows a modification of the invention of Fig. 1. r

a Fig. 3 shows a modification of the invention of Fig. 2.

Referring to Fig. 1, there is shown one type of electronic switch embodying the features of the present invention. There is provided a switching tube H, preferably of the mixer type having two independent input electrodes, vizL, control grid I2 and control grid I3. The usual suppressor grid I4 is connected to cathode l6 and a screen grid I! is provided connected to a suitable source of positive potential indicated schematically at l8, and by-passed to ground for alternating currents by the usual by-pass condenser-l9. Cathode i6 is connected to ground through a suitable cathode biasing resistor 2|, which produces a desired bias voltage for the two control grids I3 and I2.-

Control grid [2 is energized through a suitable coupling condenser 23 from one of the input voltages to be commutated, indicated as voltage A connected to terminals 22. Control or coupling resistor for grid l3. 1

grid 12 is also connected to a suitable source of positive biasing potential 24 through a grid input resistor 26. The potential of source 24 is preferably adjustable, and is suitably adjusted so as to maintain the average potential or bias on grid I2 at a value slightly negative with respect to cathode I6, and of such a value that tube ll may act as a class A amplifier for voltage A connected to input terminals 22. As will appear later, the voltage of source 24 is made adjustable to adjust the position of the cathode ray pattern corresponding to voltage A.

Control grid I3 is connected to ground through series-connected grid-current-limiting resistor 21, which ispreferably of a high value compared to the internal grid-to-cathode impedance of tube I I, and resistor 28, which serves as an input A source 29 of switching voltage is provided, which energizes a suitable transformer 3| having a center tapped secondary winding 32, 33, the center'tap 34 being grounded, as shown. Any other phase inverting device for producing two oppositely phased voltages may be used in place of transformer 3|. The switching voltage controlling the conductivity of tube H is derived from one section 33 of the secondary winding of thansformer 3|, and is connected byway of a coupling and blocking condenser 36 to the junction'point 31 of'resistors 21 and 28.

The anode 38 of switching tube H is connected'to a suitable source of positive anode potential 39 through an output resistor 4|. The output voltage of tube II is fed directly to the input grid 42 of an amplifying tube 43 by means of a'direct connection 44 between anode 38 of tube II and control grid 42. Amplifying tube 43 is'shown as comprising a conventional pentode amplifier having the usual cathode 46, screen grid 41, suppressor grid 48 and anode 49, but may be any conventional type of amplifying tube. Cathode 46 is connected to ground through suitable cathode biasingresistor 5| which provides the proper bias for control grid 42. Preferably, this resistor 5| is so chosen that the average potential of cathode 46, with respect to ground, is slightly higher than that of anode 38 and grid 42, whereby the proper bias is derived for grid 42 to permit undistorted amplification by tube 43. This is feasible, since source 51 supplying the'anode of tube 43 may have a substantially higher positive potential with respect to ground than'does source 39 supplying anode 38 of tube ll.

Screen grid '41 is connected to a suitable'sourc of positive potential 52- through a voltage-dropping resistor 53and is provided with a by-pass condenser 54. Suppressor grid 48 is connected to cathode 46 in the usual manner. Anode 49 is connected through an output resistor 56 to a suitable souroepf high positive potential 51.

Anode 49 is also directly connected. as by lead 58 to one of the deflecting plates 59 of the cathode ray tube 6|.

For the energization of the other deflecting plate '62, asecond amplifying tube 63 is provided whose cathode 64 is connected directly to cathode 46 of tube 43. In'this manner, cathode biasing resistor 5| is common to both amplifier 'tubes 43 and 63.

Control grid 66 of tube 63 is provided with grid bias in a manner which will be later described, this bias being substantially control grid 66 or tube 63 is the same as that on control grid 42 of tube 43 and is held constant while voltage A is operative to deflect the cathode ray beam. d I I Screen grid 61 of tube '63 is connected to a positive potential source, which may bethesajme as source 52, through resistor 68. Suppressor grid 69 of tube 63 is connected directly toits cathode 64 in the usual manner. Anode"lI y of grid 63 is connected to a high positive potential source, which may be the same as source 51, through its output resistor I2. Anode "'II is also connected directly as by lead '73 to the second deflecting plate 62 of cathode'ray tube 6|.

Thus, any voltage impressed upon control grid 42 of amplifier 43 will be amplified and a corresponding potential will be impressed ondeflecting plate 59. At the same time, the potential of cathode 46 will also vary in accordance with this input signal, since biasing resistor I is not by-passed. This variation of voltageacross resistor 5| produces a varying voltage between cathode 64-and control grid 66 of amplifier 63, which will thereby amplify this varying voltage. Accordingly, it will be clear that the potential of lead I3 will vary similarly to that of lead 58'. However, the variation in potential of these two leads 58, I3, and hence of deflecting plates59, 62, will be exactly in opposite senses by virtue of the phase reversal produced by means of the common cathode biasing resistor 5|. Therefore, push-pull potentials, substantially balanced with respect to'ground, are impressed; upon the deflecting plates 59 and '62 of the cathode ray tube Bl, resulting in bilateral deflections ofthe cathode ray beam. I

It is to be noted that by this method a larger variation of deflecting voltage can be produced than in the ordinary situation where one of the deflecting plates isgrounded. In the latter situation the voltage applied to the ungrounded deflecting plate must beable to swing positive and negative by the full amount of the desired defleeting potential. In the present case, however,

. 6 nested through output resistor 85 to positive source 38, and bylead to grid 66.

The second control grid 86 of tube 14 is provided with bias from an adjustable voltage source 81 (which may be the same as source 24 except when independent positioning of the cathode ray patterns is desired for the two input signals A and B) through input resistor 83, again of such value asto maintain tube 14 in a class A amplifythe equivalent-deflecting potential can be-prois completely symmetrical. In effect, the circuit comprising tubes 43 and 63 forms arr-extremely efiicient and useful phase inverter =capable of producing a substantially balanced push-pull output from any type of single voltage input. This phase inverter, of course,'is capable of wide use outside th ecircuit of the present system.

Control grid 66 of amplifier 63 is connected to the output of a second switching; tube" '14 similar in all respects to tube II already described. Thus, the cathode 16 of tube I4 is connected to ground through its biasing resistor ll. Control grid 18 is connected toground through its current-limiting resistor 19 and input resistor BI. Screen grid 82 is connected to the 'sourceof positive potential I8 and is provided with a bypass condenser 83. Suppressor grid 34 is connected directly to cathode l6. Anode 8B is coning condition. The second input signal, indicated as voltage B, is connected to terminals 89 and is led to control grid 86 through a suitable ooupling'condenser SI;

Thejunction 92 of resistors and BI is led through .a'coupling and blocking condenser 93 to the second section 32 of the secondary winding of transformer 3|, whereby a switching voltage equal to and opposite in phase to the voltage impressed at point 31 of the circuit of tube I I is impressed at point 92.

In operation, the switching voltages derived from secondaries 32 and 33 act to alternately block and unblock switching tubes II and I4. thuscausing first voltage A and then voltage B to be impressed on deflecting plates 59, 62 of cathode ray tubeGI Thus, during half cycles of the switching voltage of such a polarity that a positive potential is applied at point 31, it will be seen that grid I3 is rendered positive with respect to ground. The amplitude of switching voltage is preferably so chosen that grid I3 is also thereby rendered positive with respect to cathode I6, whereby grid'current flows between grid I 3 and cathode I6. This grid current also flows through the grid-current-limiting resistor 21, and the volt-drop thereinproduced reduces the potential of control grid I3 to a value only slightly above that of cathode l 6.

When this is done, tube II is conditioned to act as a class A amplifier, and will then amplify its input voltage A, which is thereby impressed upon control grid 42 and serves tocontrol the potentials applied to deflecting plates 59 and 62 of cathode ray tube BI in the manner already indicated.

It is to be noted that the present system is rendered substantially independent of fluctuations in-the amplitude of the switching wave above its average value so long as this amplitude is sufiicient to draw definite grid current through grid l3, and at the same time to cut-off tube 14, as will later appear, since; no matter what the amplitude of the switching voltage may be, the potential of grid I3 is caused to remain substantially unchanged with respect to cathode I6.

During these same half cycles of this switching voltage in which tube I I is conductive, a negative voltage will be applied to grid 18 of tube 14. The amplitude of'the switching voltage is also selected or adjusted so that this negative voltage applied to grid 18 will be suflicient to bias tube I4 beyond out off, whereby no electrons are permitted to flow from cathode 16 to anode and hence the plate current of tubel4 is completely out off.

During the half cycles of the switching voltage of reverse polarity, it will be clear that tubes II and 14 will interchange their conditions, that is, tube I I will become blocked, and tube M will transmit its input voltage B to the deflecting plates 59, 62 in the manner described.

Considering tube I, forthe moment, it will be clear that since during its conductive periods it operates as a class A amplifier, in which a standby or zero signal current continuously flows, the average or zero-signal potential of anode 38 will hence will have lower or even positive bias with respect to cathodes 46 and 64. This is undesirable since it creates an unbalanced condition between amplifiers 43 and 63 and may. introduce distortion. ltlwill be clearthat an opposite .nn-

balance occurs during the otherhalf cycles of the switching'voltage. These conditions produce un desired unbalance and distortion in the. cathode ray tube deflecting voltages.- I

To overcome this diillcultyit is necessary to maintain the average potential of grids 42 and 66 substantially constant during both halvesof a triode but may be of any grid-controlled type.

The cathode 99 of tube 94 is connected to ground through a suitable biasing resistor 99. The control grid IOI of tube 94 is connected to ground through series-connected resistors I02 and I03, resistor I02 serving as a grid-current-limiting resistor and resistor I03 as an input resistorior a switching voltage. sistors I02 and I03 is connected through a suitable coupling and blocking condenser I06 to secondary winding 32 of switching voltage transformer 3|, whereby grid IOI is supplied with switching voltage of phaseopposite to that supplied to control grid I3.

Thus, during the periods when tube I I is conductive, the bias on tube 94 is so selected or adjusted that the negative switching voltage applied thereto will be sufficient to bias this tube beyond cut off, whereby no current is drawn from source 39 through tube 94. During the half cycles of opposite polarity, in which tube II is blocked, the now positive switching voltage applied to grid IOI is selected of suflicient amplitude to raise the potential of grid IOI above that Of cathode 98, whereby grid current flows and resistor I02 drops the potential of grid IN to a value only slightly above that of cathode 98.

With this situation, resistor 91 is so chosen as to cause a current flowirom source 39 through resistors II and 9! and tube 94 of a value substantially equal to the stand-by or quiescent current during periods when tube II is conductive. In this manner, the average potential or bias-of grid 42 is maintainedconstant during both the conducting and blocked periods of tube II.

A similar grid-potential-controlling tube I01 is supplied for tubes I4, and acts in a similar manner to maintainthe averagepotential of grid 66 at a substantially constant value duringv the entire switching cycle, if desired. Here again it will be seen that the action of grid-potential-controlling tubes 94 and I01 is rendered substantially independent of the peak. value; of the switching voltage, thereby providing deflection controlling voltages for the deflecting plates. 59 and 62 of cathode ray tube HI I which are substantially independent of the magnitude of the switching voltage.

The junction I04 of re- It is to benoted that tubes as and 101 may be controlled to produce a difierent average potential for grids 42 and66 during the blocked condition of switching tubes II and I4 from that duringthe unblockedcondition of these tubes, if desired. a

, Itis to be noted also that the use of a balanced circuit as in the present device also causes the deflecting voltages to be substantially independ- .ent of variations in the potential of sources 39 or 57, since such variations will produce equal variationsin the same sense in the potentials of plates 59and 62, whereby the potential difierence applied between plates 59 and 62 .is not changed.

Since. the adjustable voltage: sources 24 and '8! are relatively low in voltage compared with the potential difference to be applied to the oathode ray deflection plates 59 and 62, the arrangement described provides for independently positioning the respective cathoderaypatterns by simple low voltage positioning controls. The application of such separate unidirectional pattern-positioning voltages to the switching tubes eliminates the necessity for handling the high Noltages in the cathode ray deflection plate circuits. The adjustment of the potential of the adjustable voltage source 24, for example, by varying the bias on the grid I2 of the switching rtube I I, provides for varying the average potential of bias of the grid 42 of the amplifier 43 and serves for positioning the cathode ray pattern of the cathode ray tube.

Fig. 2 shows a modification of the grid-biassisters III and H2 to which and 66. Thus, in Fig. 2 output resistor M of tube II has been split into two, P rtions I08 and I09.

In a similar fashion, outputresistor of tube .14 has been splitinto twoportions III and. I I2.

The potential of screen grid 82-oftube I4 is now derived from the junction II3 of resistors I08 and I09 to which it is directly connected. In a similar fashion, the potential of screen grid I1, tube II, is derived from the junction II4 ofreit. isfdirectly connected.

Mixer tubes, such as I I -and"'l4,f have been found to have a characteristic such that their screen grid currents are of higher value than their anode currents. Furthermore, the screen grid currents have been found to vary oppositely to the anode currents; that is, a change in input voltage such as to produce an increase in anode current will simultaneously produce a decrease in screen grid current. These characteristics are taken advan tage' of in the present circuit. Thus, during the periods when tube II is conductiveand tube 14 is blocked, the potential of'anode 38 of tube II average value of this volt drop across I 08, I09 supplies the grid bias for grid 42.

At the same time, .th-e potential for screen grid ill of tube II is provided from source 39 through resistor III. Since the screen grid current is larger than the anode current, a value ferresistor l I I may be chosen so that the screen grid current of screen grid l1 flowing through resistor II I will produce a volt-drop equal to that of the :average anode current of tube 14 flowing through resistors Ill and H2 in series during the other half of the switching cycle. In this manner, during periods when tube 14 is blocked, the potential of point H4 may be made equal to the potential of anode 80 during the periods when tube 14 is conductive, whereby the average potential of lead 95 and grid 66 of amplifier 63 remains unchanged during the whole switching cycle. In the same way, the bias of grid 42 is also keptconstant.

In the usual type of operation,screen grids ll and 82 would be by-passed completely to ground with respect to alternating" currents, whereby their potentials would remain substantially unchanged. However, if these screen grids are not completely by-passed to ground, then, by virtue of the tube characteristic just described'in which anode and screen grid currents vary equally and oppositely, it will be seen that, 'for example, during the periods when tube II is conductive and tube 14 non-conductive, a variation in anodecurrent in one sense producing a variation in the input potential of controlgrid 42 in the same sense will be accompanied by a proportional variation in screen current of 'opposite sense. which will produce a corresponding variation in the potential applied to grid 66 of tube 63 in this opposite sense, and, accordingly, the push-pull action of the common biasing resistor 5| may be assisted by the action of the screengrid currents when not by-passed to ground. In this manner, in the arrangement of Fig. 2 as in the arrange ment of Fig. 1, the same control voltage from the switching source 29 causes one cle'ctronicswitch :to be loaded when it is rendered non-conducting, and causes the other electronic" switch to be un-' loaded when it is rendered conducting, and vice rversa, in order to maintain the average output potentials of the switching tubes substantially constant.

In Fig. 2, the switching voltage'inp'ut' resistor 28 for grid 13 of tube II is connected directly to cathode l6, and corresponding'resistor'lil of tube 14 is connected to a source 60 of negative biasing potential. In this manner, when switch 30 is opened, so that the switching voltage from source 29 is no longer impressed on tubes II and 14, tube ll is rendered conductive and tube 14 non-conductive, so that switching action'is'interrupted and only voltage A is continuously applied to the cathode ray tube. If desired, of course, this same arrangement could be used in Fig. 1.

If it is desired to superpose bothvoltagesA, and B upon the deflecting plates'59. 62,. thisima'ybe' done by rendering both switching tubes If! and 14 conductive simultaneously, as by remo'v'i'ng the switching voltage and by properadjus'tme'nt of bias sources 24, 81. In this case, interaction between the two input voltages A and B would be substantially absent.

Referring once more to Fig. 1', it will be clear that if desired tubes 14 and H may have their anodes connected directly together, utilizing a common output resistor. If this is done, the necessity for the use of tubes 94 and 101- would be removed, since the average or, stand-by current will be drawn through the common output resistor by one or the other of these two tubes, depending upon which is conducting at the moment in question. In this case, input potentials would be applied to only on'eor' thelother of grids 42 and 66; theotheroithesegrids-being energized by means of the common cathode resistor 5i and provided with bias by connection to a suitable fixed bias voltage source or to two other similar switching tubes, already described.

If it is desired to impress two potentials simultaneously upon deflecting plates 56 and 6 2 without mutual reaction of these potentials one upon the other, this may be done by connecting each to a respective control grid 42 or 66 whereby the two potentials will be superposed in their effect upon deflecting plates 56 and 62 but will riot react upon one another since they are coupled only by the very high grid-to-cathode impedance of these class A amplifiers.

It is also possible to superpose two input voltages by impressing one upon the control grid, such as control grid 42, and a second upon the screen grid, such as screen grid .41, of one of the amplifier tubes, either tube 43 or 63. In this case, of course, no commutation or switching of these input voltages will be produced but they will be' superposed directly and continuously upon the deflecting plates 59 and 62 substantially without interaction. v

Also, if desired, four separate input voltages could be switched in pairs and alternately impressed in pairs upon deflecting plates 56 and 62 by the use of two pairs of, switching tubes of the type of tube I I or 74, one pair having anodes connected together and to control grid 42,- for example, and the second pair having anodes also connected together and to control grid 56*, the two tubes or each pair being alternately switched in the manner described with respect to' tubes I l and M. In this case,-as described above, tubes 94- and H11 and their associated circuits would no longer be required.

Alternatively,- four or any other number of waves may be switched in turn by appropriate switching waves applied to respective switching tubes wherebyonly one such tube is rendered conductive at a time.

Asdescribed above the circuit of Fig. 2 is useful where the screen grid currents of the vacuum tubes H and M used as switching tubes exceed their anode currents. However, under certain conditions and-for certain tubes-it is possible for the anode current to exceed the screen grid current. For such tubes it is clear that the circuit of Fig. 2 could not operate to maintain the bias ongrids and 66 at the sameilevel during both halves of the switching cycle.

Under these conditions recourse may be had to the circuit of Fig. 3, wherein are shown the anode and screen grid circuits of the tubes ill and 14 under the assumed condition that the creen a currentis lessthan the anode current; The circuitsof the remaining elements of tubes fl and 14 are not shown in Fig. 3,-but may be the same asin Fig.2-or in Fig. 1.

In this figure, thescreen; grid [1- isconnected to the anode 84 of tube ltthrough aresistor 1,2 2 and the screen grid- 82 of ,tube 14 is connectedto the anode of tube ll through a resistor I 24; Screen grids l1 and 82 are also connected directly to the amplifier tube grids fifiiand 42' by-meansof the leads and M, respectively.

Consideringnow the half cycle of the switching period in which tube !l is conductive and tube 14 is non-conductive, it willbe clear that thevariations in potential of the anode 38 of tubefl l will be conducted directly to grid 42 of amplifier1i? and that resistorlzl will'have no eifect, since no current is'drawr'i therethrough eithferbj cer um grid '42.orw screeirsnurz' astut "this latt tube being now in a blocked condition. The current for screen grid I! of tube H is drawn from source 39 through the output resistor 85 of tube H and resistor I22. By proper choice of resistor I22, the volt drop thus produced across resistors 85- and I22 by thecurrent of screen grid i! may be made equal to the quiescent volt drop across resistor- 85 when tube 14 is conductive. By so doing, the average potential of lead 95 and hence of grid 66 will be the same during the non-conduct-ive periods of tube as during the conduc- 'tive periods thereof, as is to be desired.

Similarly, the average potential of lead 44 and hence the bias on control grid 42 will be the same during both the conductive and non-conductive periods of switchingtube l I, and accordingly the same result is producedas in Fig. 2 even though the tubes II and 14 be of the type in which the screen grid current is less than the anode current.

'Also, inthe same manner as in Fig. 2, the instantaneous variations of thescreen grid current flowing through resistors 85 and l22.in the illustration used will produce corresponding variations in the potential of grid 68 and will thereby assist in the push-pull action of amplifiers 43 and 63 so that the eflects of the screen grids in Fig. 3 are the same as in Fig. 2 with regard both to maintaining bias and to assisting push-pull action. Accordingly, all remarks directed to Fig. 2 apply also to Fig. 3.

It will be apparent that by the above description there has been shown an electronic commutatingcable system capable of wide use apart from the system. of the present invention, and embodying the many advantageous features previously discussed.

As many changes could be'made in the above construction and many apparently widely different embodiments of this invention could be made without departingifrom the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 1

What is claimed is:. 1

1. A control circuit for a cathode ray tube having a pair of deflecting plates, comprising two amplifiers direct-coupled to respective ones of said deflecting plates and having a common un' bypassed cathode resistor, a pair of switching tubes having outputs including respective load resistors respectively connected to the inputs of said two amplifiers, means for applying respective control voltages to the respective inputs of said two switching tubes, means for alternately rendering said switching tubes blocked and conductive, means for maintaining the average potenmi of each of said switching tube outputs constant for both its blocked-and conductive periods, and means for individually adjusting the bias on each of said switching tubes, whereby the average potentials applied tosaid deflecting plates during said alternate periods may be individually adjusted. I

2. A control circuit fora cathode ray tube having a pair of deflecting plates, comprising two amplifiers direct-coupled to respective ones of said deflecting plates and having a common unbypassed cathode resistor, a pair of switching tubes having outputs respectively connected to the inputs of said two amplifiers, means for applying respective control voltages to the respective inputs of said switchingtubes, means for alternately and oppositelyirendering said switching tube's blocked and cond ctive whereby said deflecting plates are alternately controlled in push-pull fashion -bylsaid control voltages, and means for. individually adjusting the average values of the respective potentials applied to said deflecting plates under the control of said respective switching tubes.

3. A control circuit for a cathode ray tube having a pair of deflecting plates, comprising two amplifiers direct-coupled to respective ones of said deflecting platesand having a common unbypassed cathode resistor, means for, periodically impressing a control voltage on theinput of one of said amplifiers, means for impressing a second control voltage alternately with respect to said first voltage on theinput of the other of said amplifiers, whereby each of said voltages controls the potential of both of said plates in push-pull fashion during its respective impressed period, and means for individually-adjusting the average values of the respective potentials applied to said deflecting plates under the control'of said respective control voltages.

4. A control circuit for. a cathode ray tube having a pair of deflecting plates, comprising two amplifiers. direct-coupled to respective ones of said deflecting plates and having a common unbypassed cathode resistor, a pair of screen-grid control tubes having outputs including respective load resistors respectively connected to the inputs ofsaid two amplifiers, means for applying respective control voltages to said two control tubes, means for alternately and oppositely blocking and unblocking said control tubes, and means for maintaining the average potential of each of said control tube outputs constant'for both its blocked and unblocked periods, comprising means for passing the screen-grid current of each of said control tubes through at least a portion of the load resistor of the other of said control tubes to maintain the average output potential of said other tube at substantially the same value during both said blocked and unblocked periods.

5. A control circuit for a cathode ray tube having a pair of deflecting plates, comprising two,

amplifiers direct-coupled to'respective ones of said deflecting plates and having a common bypassed cathode resistor, a pair of switching tubes having outputs including respective load resistors respectively connected to the inputs of said two amplifiers, means for applying respective control voltages to the inputs of said two switching tubes, means for periodically rendering said switching tubes blocked and conductive, a control tube connected in parallel with each of said switching tubes, means for periodically rendering each of said control tubes blocked and conductive in synchronism with but oppositely to its respective switching tube, and means for adjusting the current drawn through said load resistors by said'control tubes to maintainthe average potential of each of said switching tube outputs constant for both its blocked and conductive periods.

6. A control circuit for a cathode ray tube having a pair of deflecting plates, comprising two amplifiers direct-coupled to respective ones of said deflecting plates and having a common unbypassed cathoderesistor, a pair of switching tubes having outputs including respective load resistors respectively connected to the inputs of said two amplifiers, means for applying respective control' voltages' to said two switching tubes, mea'nsf'for alternately blocking and unblocking said switching tubes, and means for maintaining controls the potential of both of said plates in push-pull fashion during its respective impressed period, and means for maintaining the average potential of each of said inputssubstantially constant during both impressed and non-impressed periods of said control voltages.

8. A control circuit for a cathode ray tube having a pair of deflecting plates, comprising two amplifiers direct-coupled to respective ones of said deflecting plates and. having a common unbypassed cathode resistor, a pair of switching tubes having outputs respectively connected to the inputs of said two amplifiers, means for applying respective control voltages to the respective inputs of said switching tubes, and means for alternately blocking and unblocking said switching tubes, whereby said deflecting plates are alternately controlled in push-pull fashion by said control voltages.

9. A control circuit for. a cathode ray tube having a pair of deflecting plates, comprising two amplifiers direct-coupled to respective ones of said deflecting plates and having a common unbypassed cathode resistor, means for "periodically impressing a control voltage on the input of one of said amplifiers, and means for periodically impressing a second control voltage on the input of the other of said ,ampliflersaand means for alternately rendering said voltageimpressing means effective, whereby each of said voltages controls the potential of both of said plates in push-pull fashion during its respective impressed period.

10. A control circuit for a cathode ray tube having a pair of deflecting plates for controlling the deflection of the cathode ray beam thereof, comprising an amplifier, means direct-coupling the output of said amplifier to one oi said plates, means for energizing the input of said amplifier by a control voltage, a second amplifier, means direct-coupling the output of said second amplifier to the other of said plates, a common unbypassed cathode resistor for said two amplifiers, whereby said second amplifier is energized in opposite phase from said first amplifier to produce push-pull deflection of said cathode ray beam, means for energizing the input of said second amplifier by a second control voltage, whereby both said control voltages control said beam deflection, and means for individually adjusting the average bias on said inputs, whereby the average potential of said deflecting plates due to each of said control voltages may be individually adjusted.

11. A control circuit for a cathode ray tube having a pair of deflecting plates for controlling the deflection of the cathode ray beam thereof, comprising an ampliflenmeans connecting the output of said amplifier to one of said plates, means for energizing the input of said amplifier by a control voltage, a second amplifier, means for connecting the output or said second amplifier to said'otherlplate, a common unbypassed cathode resistor 'forzsaidtwo amplifiers, whereby said second amplifier is energizedinopposite phase from firstamplifier to 'producehpush-pull deflection of said cathode ray beam, means for energizing the input-of said-second amplifier by av second, control voltage,jand means for blocking .onenor the other of said energized means.

12. A control circuit for a cathode raytube having. a pair of deflecting plates, comprising a pair of substantially identical amplifying tubes, each comprising a cathode, a control grid and an anode, means for connecting said anodes through i respective output resistors to a source of positive potential, means for connecting said anodes directly to said plates, means for biasing said grids. to substantially the same potential, means iorapplying a control potential to one of said grids, means connectingsaid cathodes together and to a common grounded andunbypassed. cathode resistor, whereby push-pull potentials are applied to said deflecting plates and the voltage across said plates is rendered substantially.independent of fluctuations in the voltage of said, source, and means for applying a second control potential to the other of said grids. i

13. .A control circuit for a cathode ray tube having a pair of deflectingplates for deflecting the. cathode ray beam thereof, comprising an amplifier, means connecting the output of said amplifier to one. of said plates, means for tenergizing the input of said amplifier by a control voltage, a second amplifier, means ior connecting the output of said second amplifier to said other plate, a common unbypassed cathode resistor for said two amplifiers, whereby said second amplifler is energized in opposite phase from said first amplifierto produce push-pull deflection of said cathode ray beam, and means for balancing the amplifiers.

14.111 an electronic switch, a pair of electron discharge tubes each having an anode and a screen grid, an output resistor connected to each of said anodes, means for alternately and oppositely rendering said tubes conductive and nonconductive, and means for maintaining the average potential oi each of said anodes at substantially the same value during both said conducting and non-conducting periods, said last means comprising a connection between the screen grid of each of said tubes to a tap of the output resistor oi the other of said tubes.

15. In an electronic switch, an electron discharge tube having a load resistor, means for periodically and alternately rendering said tube conductive and non-conductive, a control tube connected in parallel with said discharge tube and adapted when conductive to draw a current equal to the average current of said discharge tube through said load resistor during conductivity oi said discharge tube, and means for periodically and alternately rendering said control tube conductive and non-conductive oppositely to the conduction and non-conduction of said discharge tube, whereby the average output potential of said discharge tube is maintained at substantially the same value during both said conducting and non-conducting periods of said discharge tube.

16. In an electronic switch, an electron discharge tube, means for periodically and alternately rendering said tube conductive and nonconductive, and means, including a control tube .charge tube, means-for periodically and alternately rendering said tube conductive and non-.

. conductive, and means for loading said tube when it'is rendered nonconductive and unloading it when it is renderedconductive, so as to maintain the average output potential of said tube at substantiallythe same value during both said conducting and non-conducting periods.

18. An electronic switch for controlling I the transmission of a signal voltage comprising an electron discharge tube having two input grids, means for applying said signal to one of said grids to be amplified during conductive periods of said tube, a source of alternating switching voltage having amplitude at least one-half the cutoif bias of said second grid, means for applying said switching voltage to said second grid, means for biasing said cathode to a value whereby said tube is driven beyond cut oil during negative half cycles of said switching voltage and during positive half cycles said second grid is positive with respect to said .cathode, and a current limiting resistor in series with said second grid,- whereby said tube is rendered substantially independent of fluctuations in said sw'itchingvoltage.

19. An electronic switch comprising an electron discharge tube having a control grid, '2. source of alternating switching voltage connected to said grid having amplitude at least half the cut off voltage of said tube, means for biasing said tube to a value such that during positive half cycles of said switching voltage said grid is'positive with respect to said cathode and duri-ng neg ativehalf cyclessaid tubejis biased beyond cut oil, and a grid-voltage dropping resistor connected in series with said grid, whereby the operation of said tube is=rendered substantially independent of variations in the magnitude of said switching voltage.

20. An electronic switch comprising an electron discharge tube, asource of periodically varying switching .voltage,-;means for blocking said tube during half-cycles of said voltage of predetermined polarity and. for conditioning said tube to be conductive during opposite half cycles, and means for rendering said conditioning independent'iofhthe amplitude ofrsaid switching voltage. 7 V

, 21. In an electronic switch, a pair of electron discharge tubes each having an anode and a screen'grid, an .output resistor connected to each of said anodes, meansior alternately and oppositely. rendering wsaid tubes conductive and 11011! conductive, and means for maintaining the average potentialof each of said anodes at substantially the same value during both said conducting and non-conducting periods, said last means comprising a resistive connection between the screen grid-ofeach of said tubes to the anode of the other of said tubes.

. JAMES E. SHEPHERD.

CHARLES H. GUILES.

R'EFEBENCESHCIT'ED The following references are of record in the file of this patent: I

UNITED STATES PATENTS 2,265,996 Blumlein Dec. 16, 1941 OTHEIRY'VREFERENCES swam, August 1939,'- 14-17, "Trigger Circuits by Reich. 

